This section provides background information related to the present disclosure which is not necessarily prior art.
A sleeping bag typically includes first and second opposed halves defining a sleeping compartment therebetween and which are connected in such a way to define an entrance aperture at an entrance side or end of the sleeping bag. Each half of the sleeping bag includes an outer shell and an inner shell with an insulating material disposed and retained between these two layers. Insulation thickness depends on the minimum ambient air temperatures that are expected to be encountered by the user. Colder temperatures require a greater thickness of insulation to keep heat loss from the user sufficiently low enough that the user does not become uncomfortable. Sleeping bags come in several different physical configurations including, but not limited to, rectangular, semirectangular and mummy. In addition, some sleeping bags may incorporate an integral hood. Typically, sleeping bags have one or more closure devices, such as zippers, of a selected length to provide access to the entrance aperture and which can be located on the sides, ends or top to permit use of the sleeping bag.
Very lightweight, compressible insulation materials, such as water fowl down, are extremely desirable since they are able to provide sufficient insulation while being light weight and easily compressed. When used as an insulation material in sleeping bags, the down is easily compressed from the outside by the weight of the bag materials and from the inside by the user pushing outward. To assist in maintaining the insulation thickness and resist such compression, the sleeping bag can be constructed so that its outside circumference is greater than its inside circumference. This is a well-known sleeping bag construction and is normally referred to as “differential construction” or “differential cut”. Commonly, the outer shell is connected to the inner shell by baffles that create compartments or tubes into which the insulating material is placed. A sleeping bag constructed in this fashion creates an arc of insulation over the user's body. However, the are structure that is created by the differential construction has an undesirable feature. That is, the interior surface of the sleeping bag is held away from the user's body since the sleeping bag assumes the shape of the arc.